Optical irradiation with suitable energy can cool solids, a phenomenon known as optical refrigeration proposed by Pringsheim in 1929. Since the first experimental breakthrough in ytterbium-doped glasses, considerable progress has been made in various rare-earth-element-doped materials, with a recent record of cooling to 114 K directly from ambient.
The main obstacle that hinders experimental observation of laser cooling for decades in semiconductors is the low luminescence extraction efficiency. GaAs, for instance, requires a minimum extraction efficiency of 20-30% at the optimal carrier density which is difficult to achieve due to its large refractive index. One possible solution to relax the extraction efficiency challenge is to find suitable materials which have very low non-radiative recombination rates.
While the toolbox of optical refrigeration is still limited, practical applications demand more suitable materials with scalable synthesis and high cooling power density.
Accordingly, there remains an unmet need to provide for suitable materials for integration with optical refrigeration devices.